1. Field of the Invention
This invention relates to a disk cartridge rotatably accommodating therein a disk such as a magnetic disk or an optical disk. More particularly, it relates to a disk cartridge in which, for preventing the wear otherwise caused to the slide contact surfaces of a shutter mounted on the main cartridge body, surface irregularities are formed on or a lubricant is applied to these surfaces.
2. Description of the Prior Art
Up to now, as a recording medium for recording information signals, such as data signals, a magnetic disk comprised of a base member in the form of a disk-shaped thin film sheet and a magnetic layer deposited thereon as signal recording layer has been used extensively. This type of magnetic disk, however, may be damaged easily during handling since the brittle thin film is used as the base member. In addition, the slightest injury to the magnetic layer results in loss of data because of the elevated recording density of the magnetic disk.
For this reason, this type of the magnetic disk is accommodated in a main cartridge body and loaded in this state into the recording/reproducing apparatus.
The disk cartridge is provided with an opening for exposing the signal recording surface of the magnetic disk accommodated in the main cartridge body to the outside along the disk radius. The magnetic head of the recording and/or reproducing apparatus is intruded into the main cartridge body by way of the opening so as to be slidingly contacted with the magnetic disk.
Meanwhile, should the head inserting opening remain open, dust and dirt may be intruded by way of the opening into the main cartridge body to contaminate the signal recording surface of the magnetic disk. In addition, the magnetic disk may be touched during its handling by the hand or finger to contaminate similarly the signal recording surface of the magnetic disk.
For this reason, a shutter is usually provided with this type of disk cartridge for exposing the opening in the main cartridge body only when necessary, such as for recording information onto, or reading information from, the magnetic disk. This shutter is a thin plate of metal, such as stainless steel, bent into a U-shaped cross-section. The shutter is slidably mounted on the main cartridge body so as to have a slidable fit over the two major surfaces of the main cartridge body. The shutter has a window substantially coextensive with the opening in the main cartridge body and may be moved until the window is coincident with the opening.
For positively closing the opening, the shutter is formed to have a close sliding fit over the major surfaces of the main cartridge body when mounted on the main cartridge body.
It is noted that, if the shutter is formed to have a close sliding fit over the major sides of the main cartridge body, the area of relative slide contact of the shutter and the main cartridge body is increased, such that the friction of slide contact at the time of the sliding movement of the shutter is significantly increased to interfere with smooth sliding movement of the shutter.
On the other hand, the shutter formed by a metal plate, such as a stainless steel plate, is of a hardness markedly higher than that of the main cartridge body, which is molded from a resin material. Therefore, when the shutter slides synthetic resin material scrapes off the cartridge body. Besides for preventing accidental extraction of the shutter from the main cartridge body and guiding the sliding movement of the shutter, the shutter is formed with a pawl engaging in a mating groove in the main cartridge body. Since this pawl is formed by partially cutting and bending the thin metal plate, it has a sharper end face. Thus the sliding contact of the end face with the mating groove in the main cartridge body results in an increased scraping of the main cartridge body material. If such scraping occurs, the resulting chips tend to be intruded into the main cartridge body and affixed on the signal recording surface of the disk, which can cause errors during recording and reproduction of information signals.
To overcome the problem proper to the metallic shutter, it is proposed that a shutter be formed by a molded member of synthetic resin, similarly to the main cartridge body. A disk cartridge having the shutter formed of synthetic resin is disclosed, for example, in U.S. Pat. No. 4,698,714 (the '714 patent).
However, even if the shutter is formed of synthetic resin, as taught in the '714 Patent, should the shutter have a tight sliding fit over the major surfaces of the main cartridge body to provide for positive closure of the main cartridge body, the area of relative slide contact between the shutter and the main cartridge body is increased, such that the friction of sliding contact at the time of the sliding movement of the shutter is increased to interfere with smooth sliding of the shutter. Since the friction of sliding contact between the shutter and the main cartridge body is increased, scraping off of the materials of the main cartridge body and the shutter occurs after repeated usage similarly to the metallic shutter, such that the scraping chips would be introduced inevitably into the main cartridge body.